1. Field of the Invention
The present invention relates to a needle roller bearing and a bearing structure that support a crankshaft, a camshaft, a balance shaft, and a rocker shaft of a car and the like.
2. Description of the Background Art
Conventionally, as a bearing that supports a crankshaft 1 of a car and the like as shown in FIG. 6, a split type of sliding bearing has been used in general. Since the sliding bearing has high load capacity, it is suitable for being used in a high load environment.
However, as a fuel-efficient car is demanded in view of an environment recently, a needle roller bearing is used instead of the sliding bearing in some cases. Although the needle roller bearing has low load capacity as compared with the sliding bearing, since its friction resistance during rotation is small, an oil amount at a supporting part can be reduced.
However, a needle roller bearing to support a crank pin 2 of the crankshaft 1 cannot be press fitted in the axial direction. Thus, a needle roller bearing that can be used in this place is disclosed in U.S. Pat. No. 1,921,488, for example.
According to the document, the needle roller bearing comprises an outer ring, a plurality of needle rollers rotatably arranged on the raceway surface of the outer ring, and a retainer retaining the needle rollers. In addition, the outer ring comprises outer ring members 4a and 4b split by a parting line extending in the axial direction of the bearing as shown in FIG. 7, so that it can be incorporated in the crank pin 2. The same is true of the retainer.
The above needle roller bearing and a housing holding the outer ring of the needle roller bearing are separately manufactured in general. As a result, an error between a curvature radius of the outer ring and a curvature radius of the inner diameter of the housing could be generated.
When the curvature radius of the outer ring is smaller than that of the inner diameter of the housing, a gap is generated between the outer ring and the housing. Meanwhile, in a case where the curvature radius of the outer ring is larger than that of the inner diameter of the housing too much, when the outer ring is forcibly incorporated, the raceway surface of the outer ring could be undulated or damaged.
In either case, since the smooth rotation of the needle roller is hindered, a vibration or noise is generated.